牛津实用英语语法:325 must和needn’t

　　A must用于表示推论、永久命令或禁令及意向时，在间接引语中保持不变。

　　1 表示推论：

　　She said，Im always running into him;he must live near here!

　　她说：我常遇见他，他一定就住在这附近!相当于：

　　She said thathe must live in the area.

　　她说他一定就住在这附近。

　　2 表示永久命令：

　　He said，This door must be kept locked.

　　他说：这门一定要经常锁好。相当于：

　　He said that the door must be kept locked.

　　他说那门一定要经常锁好。

　　3 must在随便的话语中可表示意向，在间接引语中也保持不变：

　　He said，We must have a party to celebrate this.

　　他说：我们得开个联欢会来庆贺这事。相当于：

　　He said that they must have a party to celebrate it.

　　他说他们得开个联欢会庆贺那事。

　　B must用于表示责任时，在间接引语中可保持不变，但也可用would have to或 had to来转述。

　　1 I/we must可用would have to来转述would have to用于表示该责任取决于将来某事时或某事的完成看来很遥远或不能肯定。也就是说，在这种情况下must显然可用 will have to替代：

　　If the floods get worse we must(will have to)leave the house.he said.

　　他说：如果洪水涨得更高，我们只好离开这所房子。相当于：

　　He said that if the floods got worse they would have to leave the house.

　　他说如果洪水涨得更高，他们就得离开那所房子。

　　When it stops snowing we must start digging ourselves out，I sald.

　　我说：等雪一停，我们就得挖一条路出去。相当于：

　　I said that when it stoppd snowing we would have to start digging our- selves out.

　　我说等雪一停我们就得挖一条路出去。

　　We must mend the roof properly next year，he said.

　　他说：明年我们得把屋顶好好修理修理。相当于：

　　He said that they would have to mend the roof properly the following year.

　　他说下一年他们得把屋顶好好修理修理。

　　I have just received a letter，he said.I must go home.

　　我刚刚收到一封信，他说，我必须回家去。相当于：

　　He said that he had just received a letter and would have to go home.

　　他说他刚刚收到一封信，他得回家去。(如果他说话后立即回家了，则更常用had to，因为 had to的含义是他马上动身了。)

　　2 I/we must可用 had to转述

　　如已决定需要在某一时间完成某一动作，或已订好某一计划，或所承担的某种义务可以较快地履行完毕，或至少在转述为间接引语时已经完成了，则常用 had to表示某一必需去做的事：

　　He said，I must wash my hands.

　　他说：我得洗洗手。(他很可能后来马上去洗手了。)相当于：

　　He said that he had to wash his hands.

　　他说他得去洗洗手。

　　Tom said，I must be there by nine tomorrow.

　　汤姆说：我明天9点以前必须在那里。相当于：

　　Tom said that he had to be there by nine the next day.

　　汤姆说第二天9点以前他必须在那里。

　　在这里也可以用would have to，但这样就暗示必须做的事是

　　自己要求自己做的，而不牵涉任何外在的权威。而 had to既可以表示一种外在的权威(即有人叫他到那儿去)，也可以表示自己要求自己做的一种事。

　　当然，如果 must保持不变，则一切有关用 had to或would have to的困难都可以避免。在上面两个例子中都可以用must代替 had to或 would have to。

　　3 含有 you/he/they must的句子，也用同样方法转述：

　　He said，You must start at once.

　　他说：你必须马上出发。相当于：

　　He said that she must/had to/would have to start at once.

　　他说她必须马上出发。

　　注意：间接引语中用 would have to时，不表示说话人的权威，而只表示客观的必要。

　　Tom said，If you want to stay on here you must work harder.

　　汤姆说：你如果想继续留在这儿，就必须更努力地工作。相当于：

　　Tom said that if she wanted to stay on she must/would have to work harder.

　　汤姆说她如果想继续留在那儿，就必须更努力地工作。

　　must意味着汤姆本人坚持要她更努力地工作，而 would have to仅仅意味这么做是必要的。

　　4 含有must I/you/he?的问句也可进行同样的变化，但因为在疑问句中must常常表示目前或不久将来发生的事、所以常变为 had to：

　　Must you go so soon? I said.

　　我说：你必须走得这么急吗?相当于：

　　I asked him if he had to go so soon.

　　我问他是否必须走得那么急。

　　5 must not

　　I must not常常保持不变。 you/he must not或保持不变，或用否定意义的命令句表示：

　　He said，You mustnt tell anyone.

　　他说：你绝对不能告诉任何人。相当于：

　　He said that she mustnt tell/wasnt to tell anyone.

　　他说她绝对不能告诉任何人。

　　He told her not to tell anyone.

　　他告诉她不要告诉任何人。

　　C neednt

　　neednt可以保持不变，在一般情况下都是这样做的。另外一个办法是将它改变为 didnt have to/wouldnt have to，正如将must改变为had to/would have to一样：

　　He said，You neednt wait.

　　他说：你没必要等了。相当于：

　　He said that I neednt wait.

　　他说我没必要等了。

　　I said，If you can lend me the money I neednt go to the bank.

　　我说：如果你能借给我钱，我就不必去银行了。相当于：

　　I said that if he could lend me the money I neednt/wouldnt have to go to the bank.

　　我说如果他能借给我钱我就不必去银行了。

　　He said，I neednt be in the office till ten tomorrow morning.

　　他说：我明天上午不必在10点之前就到办公室。相当于：

　　He said that he needn t/didn t have to be in the office till ten the next morning.

　　他说他第二天上午不必在10点之前到办公室。

　　need I/you/he?的用法与must I/you/he?完全相同。即它常常变为 had to：

　　Need I finish my pudding?asked the small boy.

　　小男孩问道：我一定得把布丁吃完吗?相当于：

　　The small boy asked if he had to finish his pudding.

　　小男孩问他是否一定得把布丁吃完。